There still remains a mass of facts deserving summary notice--the oddities of inventors. Were we to collect only those that may be regarded as authentic we could make a thick volume. Despite their anecdotal character these evidences do not seem to be unworthy of some regard. It is impossible to enter here upon an enumeration that would be endless. After having collected for my own information a large number of these strange peculiarities, it seems to me that they are reducible to two categories: (1) Those inexplicable freaks dependent on the individual constitution, and more often probably also on experiences in life the memory of which has been lost. Schiller, for example, kept rotten apples in his work desk. (2) The others, more numerous, are easy to explain. They are physiological means consciously or unconsciously chosen to aid creative work; they are auxiliary helpers of the imagination. The most frequent method consists of artificially increasing the flow of blood to the brain. Rousseau would think bare-headed in full sunshine; Bossuet would work in a cold room with his head wrapped in furs; others would immerse their feet in ice-cold water (Gretry, Schiller). Very numerous are those who think "horizontally"--that is, lying stretched out and often flattened under their blankets (Milton, Descartes, Leibniz, Rossini, etc.) Some require motor excitation; they work only when walking,[26] or else prepare for work by physical exercise (Mozart). For variety's sake, let us note those who must have the noise of the streets, crowds, talk, festivities, in order to invent. For others there must be external pomp and a personal part in the scene (Machiavelli, Buffon). Guido Reni would paint only when dressed in magnificent style, his pupils crowded about him and attending to his wants in respectful silence. On the opposite side are those requiring retirement, silence, contemplation, even shadowy darkness, like Lamennais. In this class we find especially scientists and thinkers--Tycho-Brahe, who for twenty-one years scarcely left his observatory; Leibniz, who could remain for three days almost motionless in an armchair. But most methods are too artificial or too strong not to become quickly noxious. Every one knows what they are--abuse of wine, alcoholic liquors, narcotics, tobacco, coffee, etc., prolonged periods of wakefulness, less for increasing the time for work than to cause a state of hyperesthesia and a morbid sensibility (Goncourt).